Mis-configuration of the physical switch is probably the most common issue I come across when configuring virtual networking to use Jumbo Frames. The configuration varies from switch to switch – vendor to vendor. On some switches the configuration is done globally, on other switches it is configured on individual ports, and on some switches it must be enabled globally and configured per port.

Jumbo Frames must be configured correctly end-to-end. This means on the vSwitch, vmkernel interfaces, physical switches, endpoint – everything must be configured to support the larger frames end-to-end. Using larger frames will provide more efficient processing of network traffic (in many cases) but it does require a bit more complexity. If any part of the path is mis-configured, network frames larger than 1500 may not pass. If they do pass they will be fragmented, which defeats the purpose of using Jumbo Frames.
To configure Jumbo Frames on vSphere the MTU is set to 9000 on the vSwitch.

If Jumbo Frames is being used for a vmkernel service (NFS storage, iSCSI storage, vMotion, etc) the MTU is set to 9000 on the vmkernel interface.

On the ESXi Host the vmkping command can be used to test a vmkernel interface. This is useful for testing proper configuration of Jumbo Frames.

The following options are used to test Jumbo Frames configuration using vmkping:
-I Specifies the vmkernel interface to use
-d Sets the do not fragment (DF) bit on IPv4 packets – this ensures the packet will not be fragmented
-s Sets the size of the packet – to test Jumbo Frames use 8192

vHersey

Hersey Cartwright is an IT professional with extensive experience designing, implementing, managing, and supporting technologies that improve business processes. Hersey is Solutions Architect for HPE SimpliVity covering Virginia, Washington DC, and Maryland. He holds the VMware Certified Design Expert (VCDX-DV #128) certification. Hersey actively participates in the VMware community and was awarded the VMware vExpert title in 2016, 2015, 2014, 2013, and 2012. He enjoys working with, teaching, and writing about virtualization and other data center technologies. Follow Hersey on Twitter @herseyc